Research Program Area: Health & Exposure
Topic Areas: Health Effects of Air Pollution
In order to carry out meaningful risk assessments for respirable mutagenic particulate organic matter (POM), from which cost-effective control strategies can be developed, critical information is needed concerning the chemical structures of the mutagenic compounds, their concentrations in ambient POM and their pathways for formation and destruction.
In this study we carried out investigations designed to generate data addressing all three of these questions. Specifically, we collected ambient POM samples concurrently at two sites in California's South Coast Air Basin (El Monte and Riverside) and analyzed them for both chemical composition and mutagenic activity with the Ames Salmonella typhimurium bacterial assay. We also investigated the transformations of selected polycyclic aromatic hydrocarbons (PAH) adsorbed on glass fiber (GF) and Teflon-impregnated glass fiber (TIGF) filters under ambient conditions. Simultaneously, we characterized the ambient concentrations of a wide range of gaseous co-pollutants, which may participate in the atmospheric transformations and formation of ambient mutagens. In these latter measurements we employed UV/visible differential optical absorption spectroscopy (DOAS) to determine the ambient concentrations of HONO, NO3 radicals, HCHO, NO2 and SO2.
From simultaneous NO3 radical and NO2 nighttime ambient concentrations we have calculated the corresponding nighttime concentrations of dinitrogen pentoxide (N205) and we report here implications of these predicted N205 concentrations for the nighttime nitration of adsorbed, and possibly gas phase, PAH. These results also are highly relevant to the nighttime formation of nitric acid in acid rain and fogs.
Finally, we studied the formation of nitrous acid (HONO) from the hydrolysis of NO2in an indoor environment using a DOAS system especially modified and developed for this purpose. HONO is a gas phase mutagen and, by reaction with amines, a precursor to carcinogenic nitrosamines.
The following include our major findings:
* The ratios of mutagen densities for POM simultaneously collected on GF and TIGF filters were observed to vary from a low of 0.27 to a high of 4.95. The higher values occurred during periods of elevated O3 and PAN concentrations, suggesting there may be an artifact effect during particulate collection associated with one or both of these two types of filters. While analysis of the mutagen density / CO ratios suggests that a filter artifact is associated with the GF filters, we cannot rule out possible artifacts occurring on the TIGF filters. However, at the present time we prefer TIGF as the filter of choice based on its more inert properties.
* Mutagenic products were formed during exposure to ambient air of pyrene, perylene and benzo(a)pyrene, adsorbed on TIGF and GF filters. Higher mutagenicities were observed during a period of high O3 concentration (1200-1800 hr).
* For the first time 2-nitrofluoranthene and 2-nitropyrene were detected and quantified in ambient POM collected in Southern California. The presence of these nitro-PAH in ambient POM provides evidence for the transformation of certain PAH to mutagenic nitroarenes during transport through the atmosphere. Strongly mutagenic and carcinogenic (in animals) dinitropyrene isomers were also found in ambient POM collected during peak morning traffic hours. 1-nitropyrene, an animal carcinogen, was also identified in all ambient POM samples analyzed, both 2-nitropyrene and 2-nftrofluoranthene are strong direct mutagens in the Ames assay (as is1-nitropyrene) but their possible carcinogenicities are not yet known.
* Nighttime N205 concentrations were estimated for ambient atmospheres in California and in Europe, and were often found to exceed 1 ppb with calculated concentrations as high as 15-20 ppb. These predicted levels suggest that N205 may be important as an atmospheric constituent, both in nitration reactions of PAH and in the nighttime formation of nitric acid, a major component of acidic deposition.
* From an analysis of the NO3 radical, NO2, HCHO and HONO data obtained during the 1983 field study, we showed that the homogeneous gas phase mechanism proposed by Stockwell and Calvert for HONO formation (initiated by the reaction of the NO3 radical with formaldehyde) is, at most, of minor importance,
* We demonstrated for the first time that significant amounts of HONO can be formed from NO2 in an indoor environment.
These results have important consequences for our current understanding of PAH transformations and particulate mutagenicity in California's atmosphere, as well as of the formation of nitric acid in acidic rain and fogs. They also illustrate the need for further studies concerning the role of ozone and gaseous nitrogenous pollutants not only in the formation of atmospheric mutagens, but also acid deposition. Finally, they constitute relevant input into risk assessment evaluations being developed for both of these major atmospheric phenomena.
For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753
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